Next to air, water is the most important and essential, widely distributed liquid on earth. About 70% of the earth’s surface is covered by water.
Water has the ability to dissolve a large number of substances, e.g. sugar, salts etc. Water also dissolves a large number of gases including ammonia, hydrogen chloride etc. Hence, water dissolves almost every common substance and is therefore called a ‘universal solvent’.
Some terms related to solution of substances in water-
Solute- It is the substance that is dissolved in water. For e.g. sodium chloride, sugar, copper sulphate. The substance which dissolves or disappears in the solvent- i.e. liquid, to form a solution is called a solute.
Solvent- The substance which dissolves the solute e.g. water. The liquid or medium of dissolution which allows the solute to dissolve in it so as to form a solution is called a solvent.
Solution- This is the mixture of the solute and solvent. A homogeneous mixture of a solute in a solvent is called a solution.
Conditions which affect the formation of a solution-
- Solubility- of the solute in the solvent-
The solute must be soluble in the solvent for formation of a solution. For e.g. common salt dissolves in water, forming a salt solution; however, sand does not dissolve in water. Hence, no solution is formed.
- Proportion of the solute and the solvent-
The solute must be in a small amount compared to the solvent, whereas the solvent must be in a much greater amount to dissolve the solute.
- Particle size of the solute-
For quicker and complete dissolution of the solute in the solvent, the solute must be finely powdered and not be present as large crystals.
- Temperature of the solvent-
Sometimes, the solute may not be completely soluble in the solvent at normal temperatures, but upon raising the temperature of the solvent, the solute dissolves to form a solution.
Solubility of a Solute-
The maximum amount of solute in grams, which will saturate 100 gm of water at t degree C is known as the solubility of that solute in water at t degree C.
Solubility of Liquids in Water-
When liquids are able to dissolve in water, they are said to be miscible in water, and the resultant mixture is called as a miscible mixture. For e.g. alcohol and water, glycerine and water
When liquids do not dissolve in water, they are said to be immiscible in water, and the resultant mixture is called as an immiscible mixture. For e.g. oil and water, kerosene and water
Solubility of Gases in Water-
Water at normal temperatures contains dissolved gases such as oxygen. On heating, the temperature of the water increases. Inversely, the solubility of the dissolved gases decreases and they escape into the atmosphere.
Water at atmospheric pressure contains dissolved gases like oxygen. When subjected to pressure, the solubility in water of gases such as carbon dioxide increases. Under pressure, carbon dioxide dissolves in water to form a fizzy solution, commonly known as soda.